Two-sided substrate imaging using single-approach projection optics

ABSTRACT

Apparatus and method for side-by-side scanning of a substrate to use a single-approach projection optical system to provide a patterned image on each of two surfaces of a substrate panel, and more particularly a technique for pattern scanning a first surface (reverse) of the substrate panel at a reverse patterning station, flipping the substrate panel over and repositioning the substrate panel at the same or another location for patterning the opposite surface (obverse). This provides access to a both surfaces of the substrate panel for pattern scanning, and positions a second substrate panel at the first station. The flipping mechanism may be a simple grabber/retractor with a rotatable wrist. The forwarder may be a simple shuttle mechanism. Inexpensive standard pick-and-place loader/unloader mechanisms may be used for loading and unloading. To reduce the number of substrate handling mechanisms, however, it may be economical for individual robots to perform multiple substrate panel handling tasks. Relatively inexpensive special flipper/forwarder mechanisms may provide both motions of the flipper/forwarder function. In a special case, a single mechanism may carry out the entire range of loader/flipper/forwarder/unloader functions. Substrate forwarding on the stage carriage may be by pick-and-place mechanisms, slide/shuttle mechanisms or carousel mechanisms, or by a substrate docking feature which holds the substrate in place while the stage moves to a new position under the substrate panel.

(B) CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] (Not Applicable.)

(C) STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] (Not Applicable.)

(D) REFERENCE TO A MICROFICHE APPENDIX

[0003] (Not Applicable.)

(E) BACKGROUND OF THE INVENTION

[0004] (1) Field of the Invention

[0005] This invention relates to a technique to provide high-resolutionpatterned images on each of obverse and reverse (generally top andbottom) surfaces of substrate panels using single-approach projectionoptics and a scanning stage, and more particularly relates to apparatusand method for flipping the substrate over, to provide access to asecond surface of the substrate for pattern scanning, while retainingthe registration and resolution advantages of having obverse and reverseof each substrate panel patterned in quick succession with the sameprojection optics scanned by the same stage carriage.

[0006] (2) Description of Related Art

[0007] State of the art microelectronics patterning systems follow thelead of U.S. Pat. No. 4,924,257, Scan and Repeat High ResolutionLithography System, Jain, May 08, 1990. Dr. Jain teaches the use of atreated beam of laser radiation for patterning a substrate according toa mask, both mask and substrate being scanned line-by-line by a smallhexagonal field in overlapping complementary scans, for balancedillumination of the mask pattern on a photoresist on the surface of thesubstrate.

[0008] The desire to form such microlithographed patterns on bothsurfaces of a substrate, typically a thin, flat, non-flexible printedcircuit board or microchip, is both stated and solved in U.S. Pat. No.5,923,403, Simultaneous, Two-Sided Projection Lithography System, Jain,Jul. 13, 1999. Jain splits the radiation beam of a laser, and bylight-beam directing projection optical systems applies patterningradiation simultaneously through separate masks to both sides of theflat substrate. The obverse and reverse surfaces of a substrate panelare simultaneously patterned by dual optical projection systems. One ofthe optical projection systems has an up-approach, through a see-throughwindow in the stage carriage. The other optical projection system has adown-approach.

[0009] There is another way to divide the laser beam. U.S. Pat. No.5,933,216, Double-Sided Patterning System using Dual-Wavelength Outputof an Excimer Laser, Dunn, Aug. 03, 1999, splits the laser beam into twodifferent peak-power wavelengths and forwards the separated beams alongseparate optical projection systems for the two sides of the substrate.The differing wavelengths of radiation require either a broadbandphotoresist or a separate photoresist for obverse and reverse, eachoptimized for a respective one of the two wavelengths. Two substratesmay be accessed at one time, in one embodiment by up-approach anddown-approach projection optical systems—and in another embodiment byside-by-side down-approach projection optical systems, but for singlesides only of the two substrate panels.

(F) BRIEF SUMMARY OF THE INVENTION

[0010] The two-sided projection lithography systems identified aboveprovide for very high quality two-sided microelectronics patterning,mutually registered, with high throughput. They are most cost-effectivein relatively long production runs. There remains, however, a continuingdesire for simplicity and economy in two-sided high-resolutionpatterning, both aspects being economized by having single-approachoptics and a simple stage carriage, with 1:1 projection optics, for maskand substrate.

[0011] The desire continues for a simple system for high-resolutionpatterning of two-sided substrates, which has a single set of projectionoptical system, provides easy two-side registration, and is economicalfor relatively short patterning runs.

[0012] It is the object of the invention to provide, in a novelmicroelectronics patterning system, electromechanical positioners toflip the substrates for economical two-side high-resolution patterningby a single set of projection optics.

[0013] Another object of the invention is to provide a novel method forpositioning and repositioning substrates for two-sided patterning,during a single production run, by flipping the substrates forpatterning by a single-approach set of projection optics.

[0014] A feature of the invention is the use, in a simplifiedembodiment, of a single feeder/flipper/forwarder to load, flip,reposition and unload the substrate panels on the stage carriage whichprovides scanning motion of the substrates with respect to theprojection optics and the masks.

[0015] Another feature of the invention is the use, in a secondembodiment in which the economics favor separate feeders for loading andunloading, and a flipper/forwarder for repositioning the substrate afterthe first side has been patterned, for patterning the second side.

[0016] An advantage of the invention is that the costly portions of thesystem do not have to be replicated, but rather are time-shared as aresult of the inventive hardware and method.

[0017] Another advantage is that there is no need for a see-throughwindow in the stage carriage, allowing for simpler and more powerfulsubstrate grasp by vacuum.

[0018] A significant advantage in economy arises from the ease withwhich this invention can be retrofitted on existing single-approachlithography systems, by alteration of programming in the controlcomputer together with addition of relatively inexpensive flippermechanisms to existing substrate feeder mechanisms, or by replacementfeeder/flipper/forwarder mechanisms.

[0019] Other objects, features and advantages of the invention will beapparent from the following written description, claims, abstract andthe annexed drawings.

(G) BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0020]FIG. 1 is a perspective view of the system.

[0021]FIG. 2 is a partially schematic side elevation view, showing howmasks and substrate panels are gripped during patterning exposures.

[0022]FIG. 3 is a perspective view of a preferredfeeder/flipper/forwarder (loader/unloader) for the system.

[0023]FIG. 4 is a diagrammatic perspective view of flipper/forwarderflipping motions.

[0024]FIG. 5 is a schematic view of simplified flipper motions.

(H) DETAILED DESCRIPTION OF THE INVENTION

[0025]FIG. 1 is a perspective view of the system, showing projectionoptics 1 and stage 2. Stage 2 provides scanning motion with respect tooptics 1. Two masks 3 (each mask carrying a first pattern 3-1 or asecond pattern 3-2) are shown locked in place on stage 2. Stage 2 alsocarries one or two substrate panels 4 in patterning positions. Eachsubstrate panel 4 has a first (obverse) side 4 _(o) and a second(reverse) side 4 _(r). Two substrate panels SP1 and SP2 are inpatterning positions for 4 _(o) and 4 _(r) are shown. Postulate thatpatterning has been completed on both surfaces of substrate SP1, whichis ready to be removed. The usual intent is to project separate patternimages of ultraviolet radiation, patterned according to separate obversepattern mask and reverse pattern mask, onto photosensitive layers on theobverse and reverse of each substrate, to characterize a microcircuitpattern.

[0026] Procedures may vary, but the usual procedure is to:

[0027] unload/flip/forward/load substrate panels;

[0028] project the image of the obverse pattern 3 o onto obverse side 4o of the substrate panel 4 at patterning station SP1 and project theimage of the reverse pattern 3 r onto the reverse side 4 r of thesubstrate panel 4 at patterning station SP2;

[0029] then flip the substrate panel at SP1 over, preferably to a newposition, SP2, on the vacuum-operated substrate chuck carriage 5 ofstage 2; and then

[0030] project the image of the obverse pattern 3 o onto obverse side 4o of the substrate panel 4 at patterning station SP1 and project theimage of the reverse pattern 3 r onto the reverse side 4 r of thesubstrate panel 4 at patterning station SP2; and

[0031] repeat for each of the substrates SP1, SP2 . . . SPn until allsubstrates SP1, SP2 . . . SPn have been patterned on both obverse andreverse surfaces.

[0032] This procedure continues, as substrates SP1, SP2 . . . SPn are inturn loaded, patterned, flipped, patterned, and unloaded. SubstratesSP1, SP2 . . . SPn are taken from a supply/return rack 6, mounted onstage 2 carriage 5 in position for pattern imaging, patterned, flipped,patterned, unloaded and returned to supply/return rack 6. The patterningradiation beam, from laser 7, passes along beam-directing subsystem andthrough a scan path in one of masks 3 o and 3 r. (Reverse mask 3 r isshown in patterning position in FIG. 1, providing the reverse-sidepattern to substrate SP2. The patterning radiation beam is patternedaccording to the mask (mask 3 r is shown in position). The mask 3 r andreverse side of substrate SP2 are scanned line-by-line, preferably inthe overlapping complementary scans of previously cited U.S. Pat. No.4,924,257, Jain.

[0033]FIG. 1 postulates that the obverse side of substrate panel SP1 isready to be patterned according to the pattern on mask 3 _(r), and thata fully-patterned substrate panel SP0 (not shown) has been previouslyreturned to the supply/return rack 6. FIG. 1 also showsfeeder/flipper/forwarder (loader/unloader) 8 for the system, and controlunit 9. FIG. 1 shows stationary base 10, which typically is a heavyvibration-damping block which supports projection optics 1 by a bridge11-12, provides the base for the feeder/flipper/forwarder(loader/unloader) 8, supports the supply/return rack 6 and supports thebase of the stage 2.

[0034]FIG. 2 is a side elevation view, partially schematic, showing howthe substrate panels and masks are supported for presentation. Masks 3(with mask patterns 3 _(o) & 3 _(r)) and substrates (SP1, SP2 . . . SPn)are carried on mask/substrate carriage 5. Mask/substrate carriage 5 istransparent to the activating radiation in the active area of the mask.Each mask 3 is held in place by a mask chuck 13. Each mask chuck 13 isalso transparent in the active area for patterning. Substrate chuck 14,which generally is not transparent, holds the substrates in place,preferably by vacuum. Substrate chuck 14 is preferably equipped withvacuum shutoffs, and with substrate lifters or with both, to ease theprocess of unloading. Substrate lifters may be configured as simple pins15 which may be caused to rise under inactive or kerf areas of thesubstrate, lifting the substrate panel out of influence of the substratechuck vacuum, presenting the substrate panel for unloading. Thepatterning radiation passes from laser 7, through beam tunnel 16 as beam17. Beam 17 passes through the transparent window 18 and the transparentor open window of mask chuck 13, through mask 3 and projection optics 1to substrate panel 4.

Loader/Flipper/Forwarder/Unloader Robot

[0035]FIG. 3 is a perspective view of the substrate panel handlingrobot, the feeder/flipper/forwarder (loader/unloader) in a preferredembodiment. The substrate panel handling robot was not shown in FIG. 2.Other configurations of substrate-handling devices, such as air jets,rollers or edge grippers, may also be effective, depending upon type ofsubstrate, the type of substrate chuck and the type of loader/unloader.

[0036] The stage subsystem works to lock a plurality of masks andsubstrate panels (positions for two of each are shown in FIG. 1) on thecarriage 5 of the stage 2, typically by vacuum. The stage subsystem alsoworks to move those masks and substrate panels in a scanning pattern ofmotion with respect to projection optics 1, as is shown in U.S. Pat. No.5,923,403, Jain, cited above in the prior art section. A mask andsubstrate panel are scanned simultaneously, with registration guaranteedby having mask and substrate panel locked to the common stage carriage 5for simultaneous scanning motion. Preferably, scanning is by a smallhexagonal field, in the complementary overlapping mode taught by U.S.Pat. No. 4,924,257, Scan and Repeat High-Resolution Lithography System,Jain, May 8, 1990.

[0037] During repetitive operation as shown in FIG. 1, the firstsubstrate panel SP1 is shown as if it had been previously scanned on itsreverse surface, flipped over, repositioned to its present position, andscanned on its obverse surface, ready to be unloaded to thesupply/return rack 6. Substrate panel SP2 has been positioned in thereverse-side position on the stage carriage 5. The system is now shownpoised near the completion of a patterning scan of substrate panel SP2(reverse surface) according to mask 3 _(r).

[0038] After the substrate panel SP2 (reverse surface) has beenpatterned, substrate panel SP2 is flipped and repositioned forpatterning the obverse according to mask 3 o. Substrate panel SP2,during or after the flipping motion, is loaded into theobverse-patterning station for patterning of substrate panel SP1. Thisoperation continues until the production run is finished.

Method of Operation

[0039] The above discussion postulates repetitive operation during anintermediate period of the production run. The following paragraphs willgive some detail of beginning and finish of the production run.

Steps −1 & 0—Readiness, Reverse Patterning of SP2

[0040] At the beginning, (step=−1), the stage carriage 5 is empty ofsubstrate panels but has obverse-mask 3 o and reverse-mask 3 r locked intheir operative positions. A pre-load step may load a substrate panel ineach of the patterning work stations 3 o and 3 r.

[0041] Step 0 takes place after substrate panel SP2 has been loaded withits reverse surface facing the radiation beam passing through thereverse mask 3 r.

[0042] At this time the stage carriage is fully loaded with twosubstrate panels, ready for the repetitive operation discussed above,and reviewed in the paragraph following this paragraph.

Step 1—Reverse Patterning of SP2 & Obverse Patterning of SP1

[0043] There are substrate panels at the reverse-patterning work station4 r and at the obverse-patterning work station 4 o. Scanning takes placeto place pattern images 4 r and 4 o on surfaces of substrate panels SP2and SP1, respectively. When the scan has been completed, substrate panelSP1 is ready to be unloaded, substrate panel SP2 is ready to be flipped,and substrate panel SP2 is ready to be repositioned at the obverse workstation, with its obverse facing the optical beam from the appropriatemask with pattern 3 o.

Final Step—Emptying

[0044] At the finish, the reverse work station is empty and the obversework station presents the last panel in the production run, substratepanel SPn obverse, for patterning. This panel is scanned for patterning,and then unloaded, completing the production run.

Simplified Embodiments

[0045] In a super simplified embodiment, the reverse patterning stationand the obverse patterning station are not separate, but their functionsare combined at a single, two-side work station. There is preferably asingle mask, the pattern of which ordinarily must be replicated on bothsides of the substrate panel. After scanning, the substrate panel mustbe flipped (without forwarding) and repositioned, at the two-side workstation, for patterning of the other surface of the substrate panel.Loading and unloading are as discussed above.

[0046] As another alternative, the mask must be changed after each panelsurface has been scanned. This may be done manually, or may beaccomplished by a mask chuck shuttle, by a carousel or by aloader/unloader from a n adjacent mask rack.

[0047] This loader and unloader may be any of several availablesubstrate loaders which are currently marketed, or the load/unloadfunctions can be handled by the same robot which accomplishesflipper/forwarder functions.

[0048]FIG. 4 is a perspective view of a simplifiedflipper/forwarder(loader/unloader), a single all-purpose pick-and-placerobot with flipping capability. The flipper/forwarder, in thisembodiment, is also used for loading and unloading. It addresses thesubstrate panel at the reverse work station, and flips the substratepanel over as it forwards it to the obverse work station. Theflipper/forwarder preferably grasps the substrate panel by its sides orin the kerf areas, so as not to damage the photoresist layers and tostay out of the way when the substrate panel is transferred to the stageplatform. If the photoresist is protected by a transparent cover sheet,the flipper/forwarder may be a vacuum grabber that touches the coversheet.

[0049] The positioned and repositioned substrate panels may requirestandard aligning techniques prior to pattern scanning.

[0050]FIG. 4 shows the motions of a preferred flipper/forwarder robot,which moves by an in-plane sliding motion, once the stage carriage hasbeen withdrawn by stage action (or once the stage carriage has been leftbehind by vertical or horizontal motion of the robot holding thesubstrate panel). The sliding motion and the previous work station forthe substrate panel are shown in dashed lines. With sufficient clearanceabove or alongside the stage carriage, the substrate panel 30 is flippedover (inverted) and forwarded to the subsequent work station 31 as shownby the small curved arrow and the solid lines. The 180° rotation of axle32 provides the motion.

[0051]FIG. 5 shows the motions of an alternative in-station flipperrobot, which moves by an in-plane sliding motion of substrate panel 33,once the stage carriage has been withdrawn by stage action (or once thestage carriage has been left behind by vertical or horizontal motion ofthe robot holding the substrate panel. The sliding motion and theprevious location 34 of the substrate panel are shown in dashed lines.With sufficient clearance above or alongside the stage carriage, thesubstrate panel is moved out of the way of the stage carriage, flippedover (inverted) by 180° rotation of axle 35 as shown by the small curvedarrow, and returned, inverted, to the same action station (dashed lines)from the intermediate location shown by the solid lines.

[0052] Loading, positioning, forwarding and unloading the substratepanels are shown in ways suggesting pick-up and pass-off of each panel.Various slide forwarding and carousel forwarding mechanisms may also beused, with or without the cooperation of the stage carriage.

[0053] Flipping the substrate panels is shown by wrist rotation separatefrom the forwarding action. Other actions are also possible, such aselbow action or canted-loop action, where forwarding is achieved duringthe flip. If the substrate panels have sufficient flexibility, flippingand forwarding may be accomplished using a series of rollers to achievea canted-loop path. The substrate panel must be lifted off itsvacuum-locked position on the stage carriage, for the patterning of theobverse surface, and then flipped over and forwarded to the actionstation at the same or at the next substrate chuck position on the stagecarriage.

METHOD OF REPETITIVE TWO-SIDED PATTERNING

[0054] Step 1=Unload two-side finished substrate panel from obversepatterning station.

[0055] Step 2=Flip reverse-side patterned substrate panel from reversepatterning station.

[0056] Step 3=Forward to obverse patterning station for presentation ofobverse surface.

[0057] Step 4=Load blank substrate panel into reverse patterningstation.

[0058] Step 5=Scan flipped reverse-side-finished substrate panel atobverse patterning station and scan blank substrate panel at reversepatterning station. (Repeat Steps 1-5.)

[0059] [Note that Steps 2 and 3 above can be combined. See followingdiscussion.]

METHOD OF REPETITIVE TWO-SIDED PATTERNING WITH FLIPPER/FORWARDER

[0060] Step 1=Unload two-side finished substrate panel from obversepatterning station.

[0061] Step 2=Flip and forward obverse-side finished substrate panel, ina single, complex motion, with the reverse-side finished substrate panelending at the obverse patterning station, presenting substrate panelobverse-side.

[0062] Step 3=Load blank substrate panel into reverse patterningstation.

[0063] Step 4=Scan flipped reverse-side finished substrate panel atobverse patterning station and scan blank substrate panel at side-1reverse patterning station.

[0064] (Repeat Steps 1-4.)

[0065] METHOD OF REPETITIVE TWO-SIDED PATTERNING AT A SINGLE STATION,WITH FLIPPER/FORWARDER, DUAL-WAVELENGTH PHOTORESISTS, DUAL-WAVELENGTHRADIATION and TWO-MASK SHUTTLE

[0066] Preparatory Steps=Arrange blank substrates alternativelyreverse-side up and obverse-side up, reverse-side having photoresistoptimized for a first wavelength, and obverse-side having photoresistoptimized for a second wavelength, load obverse-side-up substrate inobverse patterning station and obverse-side-up substrate in obversepatterning station, pattern loaded substrates by scanning, and arrangereverse-side and obverse-side masks on a shuttle on the stage carriage;

[0067] Step 1=Unload reverse-side & obverse-side finished substratepanel, if any be present, from obverse patterning station;

[0068] Step 2=Flip and forward reverse-side-finished substrate panel, ifany be present, in a complex motion, with the reverse-side-finishedsubstrate panel ending at the obverse patterning station, presentingsubstrate panel obverse-side;

[0069] Step 3=Load blank substrate panel into obverse patterningstation;

[0070] Step 4=Scan flipped reverse-finished substrate panel at obversepatterning station and scan blank substrate panel at reverse patterningstation;

[0071] (Repeat Steps 1-4.)

[0072] Alternatively, a system can feature a substrateloader/unloader/flipper that could hold two substrates simultaneously.The operator loads two substrates onto the tool at one time, exposesboth, flips both (and transfers both substrate panels to opposite workstations in the flipping step, exposes both (opposite sides) and unloadsboth. Substrates could be arrayed alternatively, first side up/secondside up, if necessary.

1. Apparatus for repetitive two-sided mask patterning of substrates,each having obverse and reverse surfaces, using loading means, unloadingmeans, and means for inverting a substrate taken directly from asubstrate chuck on a carriage and forwarding it directly to a substratechuck on said carriage, and having a single-approach projectionsubsystem, reverse patterning station with substrate chuck, obversepatterning station with substrate chuck, and at least one mask station,comprising: a) stage mechanism with a movable carriage for providingscanning motions; and b) movable placement mechanism which has thecapability of inverting a substrate taken directly from a substratechuck on said carriage and forwarding it directly to a substrate chuckon said carriage.
 2. The method of repetitive two-sided mask patterningof substrate panels, each having obverse and reverse surfaces, usingloading means, unloading means, and flipper/forwarder means, and havingreverse patterning station, obverse patterning station and at least onemask station, each station mounted upon the traveling carriage of aprecision X-Y stage which is operable to provide scanning motion withrespect to projection optics, characterized by the following steps: Step1=Unload reverse-side finished substrate panel from reverse patterningstation. Step 2=Flip and forward obverse-side finished substrate panel,in a single, complex motion, with the obverse-side finished substratepanel ending at the side-2 work station presenting substrate panelside-2. Step 3=Load blank substrate panel into side-1 station Step4=Scan flipped obverse-side finished substrate panel at side-2 stationand scan blank substrate panel at side-1 station; (Repeat Steps 1-4). 3.The method of repetitive two-sided mask patterning of substrate panels,each having obverse and reverse surfaces, using loading means, unloadingmeans, and flipper/forwarder means, and having reverse patterningstation, obverse patterning station and at least one mask station, eachstation mounted upon the traveling carriage of a precision X-Y stagewhich is operable to provide scanning motion with respect to projectionoptics, characterized by the following steps: Step 1=Unload reverse-sidefinished substrate panel from single patterning station; Step 2=Loadblank substrate panel into single patterning station; Step 3=Scansubstrate panel reverse side at single patterning station; Step 4=Flipand replace reverse-side finished substrate panel for obverse sidepresentation at single patterning station; Step 5=(Optional) Changemask. Step 6=Scan flipped obverse-side finished substrate panel atreverse-side station. (Repeat Steps 1-6).
 4. The method of repetitivetwo-sided mask patterning of substrate panels, each having obverse andreverse surfaces, using loading means, unloading means, andflipper/forwarder means, and having reverse patterning station, obversepatterning station and at least one mask station, each station mountedupon the traveling carriage of a precision X-Y stage which is operableto provide scanning motion with respect to projection optics,characterized by the following steps: Step 1=Unload reverse-sidefinished substrate panel from side-2 station, using a movable placementmechanism; Step 2=Flip obverse-side finished substrate panel for side-2presentation; Step 3=Forward flipped obverse-side finished substratepanel to side-2 station; Step 4=Load blank substrate panel into side-1station, using said movable placement mechanism; and Step 5=Scan flippedobverse-side finished substrate panel at side-2 station; and scan blanksubstrate panel at side-1 station.
 5. The method of repetitive two-sidedmask patterning of substrate panels, each having obverse and reversesurfaces, using loading means, unloading means, and flipper/forwardermeans, and having reverse patterning station, obverse patterning stationand at least two mask stations, each station mounted upon the travelingcarriage of a precision X-Y stage which is operable to provide scanningmotion with respect to projection optics, and using two separateprojection subsystems operating with radiation beams having differentwavelengths, for said reverse patterning station and said obversepatterning station, respectively, so as to pattern at each of saidreverse patterning station and said obverse patterning station optimizedfor a different radiation wavelength, characterized by the followingsteps: Step 1=Unload both-sides finished substrate panel from obversepatterning station, using a movable placement mechanism; Step 2=Flipreverse-side finished substrate panel for obverse presentation; Step3=Forward flipped reverse-side finished substrate panel to obversepatterning station; Step 4=Load blank substrate panel into reversepatterning station, using said movable placement mechanism; and Step5=Scan flipped reverse-side finished substrate panel at obversepatterning station; and scan blank substrate panel at reverse patterningstation.
 6. The method of repetitive two-sided mask patterning ofsubstrate panels, according to claim 5, further characterized in that:the substrate panels are initially presented to the robot as twosources, one with a first set of substrate panels presenting the surfaceoptimized for a first wavelength, and the other with a second set ofsubstrate panels optimized for a second wavelength; and said loadingmeans, unloading means, and flipper/forwarder means operate on twosubstrate panels at a time for loading, for flipping and for unloading.7. The method of repetitive two-sided mask patterning of substratepanels, each having obverse and reverse surfaces, using loading means,unloading means, and flipper/forwarder means, having a single-approachprojection subsystem and at least one mask station, and having a singlepatterning station, each station mounted upon the traveling carriage ofa precision X-Y stage which is operable to provide scanning motion withrespect to projection optics, characterized by the following steps: Step1=Unload reverse-side finished substrate panel from side-2 station,using a movable placement mechanism; Step 2=Flip obverse-side finishedsubstrate panel for side-2 presentation; Step 3=Forward flippedobverse-side finished substrate panel to side-2 station; Step 4=Loadblank substrate panel into side-1 station, using said movable placementmechanism; and Step 5=Scan flipped obverse-side finished substrate panelat side-2 station; and scan blank substrate panel at side-1 station. 9.Apparatus for repetitive two-sided mask patterning of substrate panels,according to claim 8, wherein said movable placement mechanism is apick-and-place mechanism.
 10. Apparatus for repetitive two-sided maskpatterning of substrate panels, according to claim 8, wherein saidmovable placement mechanism is a slide/shuttle mechanism.
 11. Apparatusfor repetitive two-sided mask patterning of substrate panels, accordingto claim 8, wherein said movable placement mechanism is a carouselmechanism.